Phase-corrector

ABSTRACT

The signal to be corrected in phase is applied in phase quadrature to a first channel comprising a linear attenuator and to a second channel comprising two diodes connected in parallel and in reverse directions as concerns the input a-c current of this channel and in series as far as the bias is concerned, the two diodes receiving from a source the same bias voltage. The output signals from the two channels are added in an adder.

United States Patent 1191 I Bareyt Nov. 19, 1974 PHASE-CORRECTOR 3,148,285 9/1964 Tedeschi et a1 328/155 x 3, 2, 7 l 197 F 28 [75] Inventor: Claude Bare", Pans France 3,226,226 1211978 P31; 30715; [73] Assignee: Thomson-CSF, Paris, Fra 3,760,219 9/1973 De Santis et a1 315/35 [22] Med: 1973 Primary Examiner-John S. Heyman [21] Appl. No.: 406,862 Attorney, Agent, or FirmCushman, Darby &

, Cushman [30] Foreign Application Priority Data 0m. 20, 1972 France 72.37262 ABSTRACT v The signal to be corrected in phase is applied in phase [52] US. Cl 307/295, 328/155, 328/55, quadrature to a first channel comprising a linear anew I t Cl 330/43 315/35 333/29 uator and to a second channel comprising two diodes connected in parallel and in reverse directions as con- [58] Fleld of Search 315/35; 330/43; 328/55 cerns the input a-c current of this channel and in se- 328/56 155; 307/317 295; 333/29 ries as far as the bias is concerned, the two diodes receiving from a source the same bias voltage. The out- [56] References C'ted put signals from the two channels are added in an ad- UNITED STATES PATENTS d 2,945,949 7/1960 Jauernik 328/55 2,984,799 5/1961 Gerks 328/155 X 4 Clam, 6 D'awmg V 0 LT A GE 5 0 1.1 R CE 1 t E M n COUPLER '1 '1 2 7 6 5O 2 1 1o 1 S VOLTAGE 3 AUDER S 0 U R C E 5 '5 12 5:7 i

PATENI'L 1 3V 1 91874 SHEET 10F 2 FIG.2

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21 VOLTAGE SOURCE I L M V k -L 20 5 AUDER VOLTAGE SOURCE PATENT'LU fi 1 91914 3; 849.676

SHEU 2 OF 2 108 50 E PHASE voLT E i m nvmms CORRECTOR SOURCE WAVE TUBE PHASE-CORRECTOR Thepresent invention relates to phase-correctors, in particular although not exclusively, for the precorrection of frequency-modulated signals intended for application to a travelling wave tube or to other non-linear devices giving rise to phase and amplitude distortions of the same kind. 1

Those skilled in the art will appreciate that travellin wave tubes have a phase characteristic (phase lag created as a function of the input power P,) of the kind indicated for example in FIG. 1, which is the characteristic taken from a 25 watt tube operating at a carrier frequency in the order of 6,000 mc/s, the phase lag increasing with input power. This lag d) is given in degrees and the power P in decibels relatively to the reference level of 1 mW. These tubes on the other hand have an output power P /input power P characteristic of the kind illustrated in FIG. 2, which is a characteristic taken from the same tube as that of FIG. 1, P and P being given again relatively to the reference level of 1 mW. The output power reaches a saturation value P for a given value P of the input power. The output amplitude/input amplitude characteristic obviously exhibits a corresponding saturation level.

In practice, at least as long as the tube is not operated at less than 6 db below its saturation level, the phasedistortion is generally the greatest source of nuisance in practical applications, applications such for example as the amplification, by means of a travelling wave tube, of a signal frequency-modulated by a multiplex telephone signal.

It has been proposed, to effect precorrection .of the signal prior to amplification, a phase-correcting device comprising two channels which receive the signal to be corrected with the same amplitude and in phase quadrature, the first of the channels being linear, the'second containing a non-linear device formed by a series of attenuators, each of which is constituted by a PIN diode non-linearly attenuating its input signal in accordance with the law determined by the diode characteristic, and by a variable bias voltage produced by detection of part of this input signal.

The Applicants have found that satisfactory results can be achieved in a simpler and more economic way.

According to the invention, there is provided a phase corrector comprising means, having first ancl second terminals, for applying an input signal in phase quadrature to said first and second terminals, the signal appearing at said first terminal lagging in phase relatively to the signal appearing at said second terminal; a linear attenuator coupled to said first terminal; a non-linear channel coupled to said second terminal and including a non-linear device comprising a d-c series arrangement of two diodes, said two diodes being connected in the same direction relatively to a d-c current applied to said series arrangement, and being coupled in parallel and in reverse directions relatively to the a-c current appearing at said second terminal, means for biasing said diodes by the same d-c voltage value and in the same direction, and an adder for adding together the output signals from said linear attenuator and from said non-linear channel.

The invention likewise relates to an amplifier device 6 the ensuing description and the related drawing in which:

FIGS. 1 and 2 already described, are graphs showing a pratical example of the phase and amplitude distortions produced by a travelling wave tube.

FIG. 3 is a diagram of an embodiment of a phasecorrector in accordance with the invention.

FIGS. 4 and 5 are diagrams illustrating the operation of the phase corrector shown in FIG. 3.

FIG. 6 is a travelling wave tube amplifier circuit, utilising a phase-corrector device in accordance with the invention.

In FIG. 3, a 3 db coupler 30, that is to say a 3 db coupler whose outputs are in phase-quadrature, is supplied at its input E with the input signal and produces at its two outputs l and 2 two signals, the output 1 delivering a signal lagging in phase by 90 in relation to the signal appearing at the output 2. The output 1 supplies a linear attenuator, preferably an adjustable one. This attenuator, in the present example, utilises as an adjustable resistive element, a PIN diode 3 biased by an adjustable constant voltage supplied by a source 21, the diode 3 and the source 21 being connected in parallel between ground and the common terminal M of two capacitors 41 and 42 connected in series, the other terminal of the capacitor 41 forming the input of the linear channel and the other tenninal of the capacitor 42 the output of this channel.

The source 21 comprises a device, for example a choke coil, which prevents the a.c. circuit from closing across the source.

The output 2 of the coupler constitutes the input of the non-linear channel. It is connected, respectively, through two capacitors 4 and 5 to the anode of a diode 6 and to the cathode of a diode 7. The diodes 6 and 7 will for example be Schottky diodes. The cathode of the diode 6 and the anode of the diode 7 are connected to the first terminal of a capacitor 8 whose second terminal forms the output of the non-linear channel. By means of a voltage source 20 (equipped with an a.c. blocking device in the same way as the source 21) a d-c potential difference of 2U is applied between the terminal 11, common to the capacitor 4 and the diode 6, and the terminal 12, common to the capacitor 5 and the diode 7; this has the effect of applying a d-c voltage U between anode and cathode of each diode. The output of the non-linear channel and that of the linear channel, respectively supply the two inputs of an adder 10 whose output S is the output of the phase-corrector.

In FIG. 4, a vectorial illustration of the output signals A,, A A and B B and B from the linear and nonlinear channels respectively of the phase-corrector, has been given in respect of three input signals having different amplitudes but the same frequency and the same phase, V V V The corresponding output signals W W and W;, from the phase-corrector have also been shown.

It has been assumed that the linear attenuator and the non-linear channel have attenuated signal V in the same ratio. The linear channel and the non-linear channel thus, in respect of the signal V produce two signals A and B of the same amplitude, in phase quadrature, the resultant W of which has a phase lead of 45 in relation to the phase of the signals A,, A and A If the smallest of the input signals, V has been more attenuated by the non-linear channel than by the linear channel, the corresponding output signal W will, in relation to the phase (1),, have a phase lead of less than 45, and if the largest of the three input signals has been less attenuated by the non-linear channel than by the linear channel, it will have a lead of more than 45 in relation to (b More generally, if the non-linear device compresses the low-amplitude signals in relation to the highamplitude ones, or in other words if it behaves as an expander vis-a-vis high amplitudes, at the output of the phase corrector a signal will exhibit phase leads in relation to the signals having smaller amplitudes, thus making it possible to correct the kind of phase distortion which is illustrated by the graph shown in FIG. 1.

To do this, of course, it is necessary to adjust the amplitude-amplitude characteristic of the non-linear channel.

FIG. 5 illustrates how this may be done in a simple manner. In FIG. 5, the curve X which is symmetrical in relation to represents the input voltage U output current I characteristic of the non-linear channel in the absence of application of any bias to the two diodes. If, by means of the source 20, a voltage difference 2 U is applied between the terminals 11 and 12, in

order to apply a bias voltage of U to each of the two diodes, then for U positive U,,, a characteristic Y is obtained. If U is negative, U U each of the diodes is biased in the reverse direction and a characteristic Z is obtained. In the drawing, it has been assumed that U U,,/2.

Thus, by acting on the direction and value of the bias, it is a simple matter to obtain an amplitude-amplitude curve which will give satisfactory phase-correction within the range of amplitudes of the considered signal as delimited for example by the straight lines yy and zz,. With the travelling wave tube to which the characteristics plotted in FIGS. 1 and 2 relate, it has been possible, using the extremely simple phase-corrector shown in FIG. 3, to reduce from 40 to 8 the variation in phase exhibited by the output signal from the tube in respect of an input power variation of 20 db. This introduces an amplitude distortion in relation to the input signals but that is something which is not of high importance in a great many cases. Moreover, in the amplifier device more particularly referred to, the amplitude distortion introduced by the phase-correcting device, as a look at the graph of FIG. 2 shows, is in the reverse direction to that introduced by the travelling wave tube. In fact, what happens in practice is partial correction and not over-compensation.

It is also possible, in a manner known per se, to have the phase-corrector followed by an amplitudecorrector so that as far as the amplitude is concerned, the superimposed effects of the amplitude distortions introduced by the phase-corrector, the amplitudecorrector and the travelling wave tube, compensate one another in a satisfactory manner. It is possible to utilise, as an amplitude-corrector, a circuit identical to that which constitutes the non-linear channel of the phase-corrector, with an appropriate bias voltage.

FIG. 6 illustrates an amplifier device of this kind. The block 100 represents the phase-corrector of FIG. 3, the output of which supplies an amplitude-corrector which is a circuit identical, apart from the value of the bias, to that of the non-linear channel of the phase-corrector device shown in FIG. 3, the corresponding elements being represented by the same reference numbers but increased by 100. The output of the capacitor 108 of the amplitude-corrector is connected to the input of a travelling wave tube 50.

Self-evidently, the phase-corrector may be improved through forming its non-linear channel by the series arrangement of two or more circuits of the kind constituting the non-linear channel in the phase-corrector shown in FIG. 3; the value of the bias 2 U may then differ for the different circuits.

A similar remark applies to the amplitude-corrector.

. minal lagging in phase relatively to the signal appearing at said second terminal; a linear attenuator coupled to said first terminal; a non-linear channel coupled to said second terminal and including a non-linear device comprising a d-c series arrangement of two diodes, said two diodes being connected in the same direction relatively to a dc current applied to said series arrangement, and being coupled in parallel and in reverse directions relatively to the a-c current appearing at said second terminal, means for biasing said diodes by the same d-c voltage value and in the same direction, and an adder for adding together the output signals from said linear attenuator and from said non-linear channel.

2. A phase-corrector as claimed in claim 1, wherein said linear attenuator is constituted by a PIN diode and means for applying a d-c bias voltage to said PIN diode.

3. An amplifying arrangement for a frequency modulated signal, comprising, in a series arrangement, two correctors followed and a travelling wave tube, one of said correctors being a phase corrector and the other one being an amplitude corrector, said phase corrector comprising means, having an input and first and second output terminals, for applying an input signal in phase quadrature to said first and second terminals, the signal appearing at said first terminal lagging in phase relatively to the signal appearing at said second terminal; a linear attenuator coupled to said first terminal; a nonlinear channel coupled to said second terminal and including a non-linear device comprising a do series arrangement of two diodes, said two diodes being connected in the same direction relatively to a d-c current applied to said series arrangement, and being coupled in parallel and in reverse directions relatively to the a-c current appearing at said second terminal, means for biasing said diodes by the same d-c voltage value and in the same direction, and an adder for adding together the output signals from said linear attenuator and from said non-linear channel.

4. An amplifying arrangement as claimed in claim 3, wherein said amplitude corrector comprises a dc series arrangement of two diodes, said two diodes being connected in the same direction relatively to a d-c current applied to said series arrangement, and being coupled in parallel and in reverse directions relatively to the a-c current of the input signal, and means for biasing said diodes by the same d-c voltage value and in the same direction. 

1. A phase corrector comprising means, having an input and first and second output terminals, for applying an input signal in phase quadrature to said first and second terminals, the signal appearing at said first terminal lagging in phase relatively to the signal appearing at said second terminal; a linear attenuator coupled to said first terminal; a non-linear channel coupled to said second terminal and including a non-linear device comprising a d-c series arrangement of two diodes, said two diodes being connected in the same direction relatively to a d-c current applied to said series arrangement, and being coupled in parallel and in reverse directions relatively to the a-c current appearing at said second terminal, means for biasing said diodes by the same d-c voltage value and in the same direction, and an adder for adding together the output signals from said linear attenuator and from said non-linear channel.
 2. A phase-corrector as claimed in claim 1, wherein said linear attenuator is constituted by a PIN diode and means for applying a d-c bias voltage to said PIN diode.
 3. An amplifying arrangement for a frequency modulated signal, comprising, in a series arrangement, two correctors followed and a travelling wave tube, one of said correctors being a phase corrector and the other one being an amplitude corrector, said phase corrector comprising means, having an input and first and second output terminals, for applying an input signal in phase quadrature to said first and second terminals, the signal appearing at said first terminal lagging in phase relatively to the signal appearing at said second terminal; a linear attenuator coupled to said first terminal; a non-linear channel coupled to said second terminal and including a non-linear device comprising a d-c series arrangement of two diodes, said two diodes being connected in the same direction relatively to a d-c current applied to said series arrangement, and being coupled in parallel and in reverse directions relatively to the a-c current appearing at said second terminal, means for biasing said diodes by the same d-c voltage value and in the same direction, and an adder for adding together the output signals from said linear attenuator and from said non-linear channel.
 4. An amplifying arrangement as claimed in claim 3, wherein said amplitude corrector comprises a d-c series arrangement of two diodes, said two diodes being connected in the same direction relatively to a d-c current applied to said series arrangement, and being coupled in parallel and in reverse directions relatively to the a-c current of the input signal, and means for biasing said diodes by the same d-c voltage value and in the same direction. 